Permanent magnet rotating electric machine

ABSTRACT

A permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this rotating electric machine, the permanent magnets are convex V-shaped or U-shaped with respect to a rotor axis. Moreover, nearly V-shaped recess portions, each of which is placed between adjacent poles, are formed in outer circumferential surface portions of the rotor core. Thus, torque caused by magnetic flux due to the magnets is increased, while armature reaction magnetic flux generated by an armature current is reduced. Consequently, q-axis inductance is reduced, so that armature current commutation is quickly achieved. Thus, the permanent magnet rotating electric machine using the stator employing concentrated windings and also using the magnet-embedded rotor is stably driven even when driven by a position sensorless inverter in the case of 120 degree energization.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a permanent magnet rotating electric machine and, more particularly, to a permanent magnet rotating electric machine to be mounted on a compressor of an air conditioner.

[0003] 2. Description of the Related Art

[0004] Hitherto, such kinds of permanent magnet rotating electric machines have employed permanent magnets of various shapes. For example, Japanese Unexamined Patent Application Publication No. 6-339241 describes a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, thereby enhancing an output of the rotating electric machine by utilizing reluctance torque.

[0005] The aforementioned conventional permanent magnet rotating electric machine comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, thereby enhancing the efficiency of the rotating electric machine by effectively utilizing reluctance torque.

[0006] However, the conventional permanent magnet rotating electric machine has a drawback in that the adoption of the concentrated windings results in reduction in an effective range of induced voltages, and that when the rotating electric machine is driven by a position sensorless inverter in the case of 120 degree energization, a position sensor signal due to the induced voltage is not obtained and thus the rotating electric machine is out of working order.

[0007] Accordingly, an object of the present invention is to provide a permanent magnet rotating electric machine using a stator employing concentrated windings and a magnet-embedded rotor, which can be stably driven even when driven by a position sensorless inverter in the case of 120 degree energization.

SUMMARY OF THE INVENTION

[0008] To achieve the foregoing object, according to an aspect of the present invention, there is provided a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this machine, each pair of adjacent ones of permanent magnets is arranged like a convex V or the permanent magnets are convex and U-shaped with respect to a rotor axis. Moreover, a nearly V-shaped recess portion is formed between adjacent poles in outer circumferential surface portions of the rotor core.

[0009] Further, according to another aspect of the present invention, there is provided a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this machine, each pair of adjacent ones of the permanent magnets is arranged like a convex V or the permanent magnets are convex and U-shaped with respect to a rotor axis. Moreover, a nearly V-shaped recess portion is formed between adjacent poles in outer circumferential surface portions of the rotor core. Furthermore, a plurality of slits radially extending in the rotor are formed in an outer circumferential portion, which is located outwardly from the permanent magnets, of the rotor core.

[0010] Moreover, according to another aspect of the present invention, there is provided a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this machine, a slit radially extending in the rotor is formed in a central portion of each of the teeth of the stator core. Further, each pair of adjacent ones of permanent magnets is arranged like a convex V or the permanent magnets are convex and U-shaped with respect to a rotor axis. Moreover, a nearly V-shaped recess portion is formed between adjacent poles in outer circumferential surface portions of the rotor core.

[0011] According to another aspect of the present invention, there is provided a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this machine, a slit radially extending in the rotor is formed in a central portion of each of the teeth of the stator core. Further, each pair of adjacent ones of the permanent magnets is arranged like a convex V or the permanent magnets are convex and U-shaped with respect to a rotor axis. Moreover, a nearly V-shaped recess portion is formed between adjacent poles in outer circumferential surface portions of the rotor core. Furthermore, a plurality of slits radially extending in the rotor are formed in an outer circumferential portion, which is located outwardly from the permanent magnets, of the rotor core.

[0012] To achieve the foregoing object, according to another aspect of the present invention, there is provided a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this machine, each pair of adjacent ones of the permanent magnets is arranged like a convex V or the permanent magnets are convex and U-shaped with respect to a rotor axis. Moreover, a plurality of nearly V-shaped recess portions, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of the rotor core.

[0013] Further, according to another aspect of the present invention, there is provided a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this machine, each pair of adjacent ones of the permanent magnets is arranged like a convex V or the permanent magnets are convex and U-shaped with respect to a rotor axis. Moreover, a plurality of nearly V-shaped recess portions, each of which is placed between adjacent poles, are formed in outer circumferential surface portions of the rotor core. Furthermore, a plurality of slits radially extending in the rotor are formed in an outer circumferential portion, which is located outwardly from the permanent magnets, of the rotor core.

[0014] Moreover, according to another aspect of the present invention, there is provided a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this machine, each pair of adjacent ones of the permanent magnets is arranged like a convex V or the permanent magnets are convex and U-shaped with respect to a rotor axis. Moreover, a plurality of nearly L-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of the rotor core.

[0015] According to another aspect of the present invention, there is provided a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this machine, each pair of adjacent ones of the permanent magnets is arranged like a convex V or the permanent magnets are convex and U-shaped with respect to a rotor axis. Further, a plurality of nearly L-shaped recess portions, each of which is placed between adjacent poles, are formed in outer circumferential surface portions of the rotor core. . Furthermore, a plurality of slits radially extending in the rotor are formed in an outer circumferential portion, which is located outwardly from the permanent magnets, of the rotor core.

[0016] To achieve the foregoing object, according to another aspect of the present invention, there is provided a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this machine, a slit radially extending in the rotor is formed in a central portion of each of the teeth of the stator core. Further, each pair of adjacent ones of the permanent magnets is arranged like a convex V or the permanent magnets are convex and U-shaped with respect to a rotor axis. Moreover, a plurality of nearly V-shaped recess portions, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of the rotor core.

[0017] Further, according to another aspect of the present invention, there is provided a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this machine, a slit radially extending in the rotor is formed in a central portion of each of the teeth of the stator core. Further, the each pair of adjacent ones of the permanent magnets is arranged like a convex V or the permanent magnets are convex and U-shaped with respect to a rotor axis. Moreover, a plurality of nearly V-shaped recess portions, each of which is placed between adjacent poles, are formed in outer circumferential surface portions of the rotor core. Furthermore, a plurality of slits radially extending in the rotor are formed in an outer circumferential portion, which is located outwardly from the permanent magnets, of the rotor core.

[0018] Moreover, according to another aspect of the present invention, there is provided a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this machine, a slit radially extending in the rotor is formed in a central portion of each of the teeth of the stator core. Further, each pair of adjacent ones of the permanent magnets is arranged like a convex V or the permanent magnets are convex and U-shaped with respect to a rotor axis. Moreover, a plurality of nearly L-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of the rotor core.

[0019] According to another aspect of the present invention, there is provided a permanent magnet rotating electric machine that comprises a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core. In this machine, a slit radially extending in the rotor is formed in a central portion of each of the teeth of the stator core. Further, each pair of adjacent ones of the permanent magnets is arranged like a convex V or the permanent magnets are convex and U-shaped with respect to a rotor axis. Moreover, a plurality of nearly L-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of the rotor core. Furthermore, a plurality of slits radially extending in the rotor are formed in an outer circumferential portion, which is located outwardly from the permanent magnets, of the rotor core.

[0020] In the permanent magnet rotating electric machine of the present invention, a convex portion core may be placed between nearly V-shaped or L-shaped concave portions formed in outer circumferential surface portions of the rotor core. Moreover, the width of an innermost-circumference-side part of the convex portion core may be made to be larger than an outermost-circumference-side circumferential distance between the permanent magnet inserting holes.

[0021] Incidentally, let θ₂ denote an angle between segments respectively drawn from the rotor axis to both points of intersection of the outer circumferential surface of the rotor core 8 and the V-shaped or L-shaped recess portion. Further, let θ₄ designate a value obtained by dividing 360 (deg.) by the number of poles. In one of the aforementioned permanent magnet rotating electric machines, preferably, a ratio (θ₂/θ₄) is set so that 66.7%≦(θ₂/θ₄)≦85.7%.

[0022] When the rotating electric machine is driven by using the position sensorless inverter in the case of 120 degree energization, a rotor position is detected by sensing an induced voltage in the rotating electric machine. That is, differently from a 120-degree energization section, an induced voltage appears between the terminals of the rotating electric machine in a 30-degree non-energization section. The rotor position is detected from a zerocross point thereof.

[0023] An armature current flows through the windings. Thus, it is necessary to perform commutation thereof in the 30 degree non-energization section. However, the concentrated windings have high inductance. Moreover, the range of induced voltages is narrow. Thus, the armature current cannot quickly be reduced.

[0024] As a countermeasure against this, it is considered that the inductance of the wirings is reduced.

[0025] However, the leakage inductance of the windings themselves are regulated owing to the structural conditions. Moreover, the magnitude thereof is low. Therefore, it is sufficient for reducing the inductance of the windings to reduce inductance called “q-axis inductance”, which is generated according to the coupling between the rotor core and the armature windings.

[0026] The present invention is based on this principle. The leakage magnetic flux of the permanent magnets is reduced by arranging the permanent magnets like convex Vs with respect to the rotor axis and by providing nearly V-shaped recess portions each of which is formed in the outer circumferential portion of the rotor core and between adjacent poles. Thus, torque due to magnetic flux generated by the permanent magnets is increased. Moreover, armature reaction magnetic flux produced by an armature current is reduced.

[0027] Thus, the q-axis inductance decreases. Furthermore, the armature current commutation is quickly achieved. Consequently, according to the present invention, there is provided a permanent magnet rotating electric machine that can stably be driven even when the electric machine is driven by the position sensorless inverter in the case of 120 degree energization.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Other features, objects and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the drawings in which like reference characters designate like or corresponding parts throughout several views, and in which:

[0029]FIG. 1 is a radially sectional view of a permanent magnet rotating electric machine according to a first embodiment of the present invention;

[0030]FIG. 2 is an enlarged radially sectional view of a rotor 7 shown in FIG. 1;

[0031]FIG. 3 is a graph illustrating the characteristics of the rotating electric machine according to the first embodiment of the present invention;

[0032]FIG. 4 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to a second embodiment of the present invention;

[0033]FIG. 5 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to a third embodiment of the present invention;

[0034]FIG. 6 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to a fourth embodiment of the present invention;

[0035]FIG. 7 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to a fifth embodiment of the present invention;

[0036]FIG. 8 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to a sixth embodiment of the present invention;

[0037]FIG. 9 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to a seventh embodiment of the present invention; and

[0038]FIG. 10 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to an eighth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] First Embodiment

[0040]FIG. 1 is a radially sectional view of a permanent magnet rotating electric machine according to a first embodiment of the present invention. In the first embodiment, a stator 6 of a permanent magnet rotating electric machine 1 comprises a stator core 2, and armature windings 5 wound in a plurality of slots 4 that are formed in the stator core 2 together with teeth 3. The armature windings 5 include concentrated U-phase windings 5A, concentrated V-phase windings 5B, and concentrated W-phase windings 5C. The rotor 7 of the permanent magnet rotating electric machine 1 comprises a rotor core 8, and permanent magnets 10, each pair of adjacent ones of which are respectively placed in permanent magnet inserting holes 9 that are arranged like a letter “V” and formed in the rotor core 8. A shaft fitting hole 11, into which the shaft (not shown) is fitted, is formed in the rotor core 8. Incidentally, the permanent magnets 10 are arranged therein so that the first embodiment has a four-pole stator.

[0041]FIG. 2 is an enlarged radially sectional view of the rotor 7 shown in FIG. 1. As shown in FIG. 2, rivet holes 12 for fixing the rotor core 8, and V-shaped recess portions 13 provided between the adjacent permanent magnets arranged like a letter “V” are formed in the rotor 7.

[0042] Incidentally, let θ₂ denote an angle between segments respectively drawn from the rotor axis to both points of intersection of the outer circumferential surface of the rotor core 8 and the V-shaped recess portion. Further, let θ₁ denote an angle between segments respectively drawn from the rotor axis to both the outermost-circumferential-side inner end surfaces 9 of the adjacent inserting holes arranged like a letter “V”. The rotor 8 is configured so that θ₁<θ₂. Furthermore, let θ₄ designate a value obtained by dividing 360 (deg.) by the number of poles. In this case, the first embodiment is set so that 66.7%≦(θ₂/θ₄)≦85.7%.

[0043]FIG. 3 is a graph illustrating the characteristics of the rotating electric machine according to the first embodiment of the present invention. Abscissas represent the ratio (θ₂/θ₄) normalized by assuming that the value of this ratio is 100% when the recess portions 13 are not provided. Ordinates represent motor efficiency normalized by assuming that the efficiency is 1.0 pu. FIG. 3 also shows a result of study performed on commutation quality.

[0044] Regarding the commutation quality, a white circle indicates a state in which a position sensor signal due to an induced voltage is stably obtained and the waveform of an armature current is stable during the rotating electric machine is driven by a position sensorless inverter in the case of 120 degree energization. In contrast, a cross indicates a state in which the intervals of position sensor signals due to induced voltages are not uniform and a peak appears in the waveform of the armature current and the rotating speed is unstable during the rotating electric machine is driven by the position sensorless inverter in the case of 120 degree energization.

[0045] Results shown in FIG. 3 reveal that when the ratio (θ₂/θ₄) is 100% or 90%, a commutation operation is unstable, and the motor efficiency is enhanced by providing the recess portions 13 in the rotor 7.

[0046] In contrast, when the ratio (θ₂/θ₄) is 85.70%, a commutation operation is stable, and providing the recess portions 13 therein enhances the motor efficiency.

[0047] When the rotating electric machine is driven by using the position sensorless inverter in the case of 120 degree energization, a rotor position is detected by sensing an induced voltage in the rotating electric machine. That is, differently from a 120-degree energization section, an induced voltage appears between the terminals of the rotating electric machine in a 30-degree non-energization section. The rotor position is detected from a zerocross point thereof.

[0048] An armature current flows through the windings. Thus, it is necessary to perform commutation thereof in the 30 degree non-energization section. However, the concentrated windings have high inductance. Moreover, the range of induced voltages is narrow. Thus, the armature current cannot quickly be reduced.

[0049] As a countermeasure against this, it is considered that the inductance of the wirings is reduced.

[0050] However, the leakage inductance of the windings themselves are regulated owing to the structural conditions. Moreover, the magnitude thereof is low. Therefore, it is sufficient for reducing the inductance of the windings to reduce inductance called “q-axis inductance”, which is generated according to the coupling between the rotor core and the armature windings.

[0051] The first embodiment is based on this principle. The leakage magnetic flux of the permanent magnets 10 is reduced by arranging the permanent magnets like convex Vs with respect to the rotor axis and by providing nearly V-shaped recess portions each of which is formed in the outer circumferential portion of the rotor core and between adjacent poles. Thus, torque due to magnetic flux generated by the permanent magnets is increased. Moreover, armature reaction magnetic flux produced by an armature current is reduced.

[0052] Thus, the q-axis inductance decreases. Furthermore, the armature current commutation is quickly achieved. Consequently, according to the present invention, there is provided a permanent magnet rotating electric machine that can stably be driven even when the electric machine is driven by the position sensorless inverter in the case of 120 degree energization.

[0053] Further, the experiments reveals that as the ratio (θ₂/θ₄) is gradually reduced from 75.5% to 55% through 66.7%, the commutation operation becomes stable more and more, and that a limit point, at which the motor efficiency also decreases, appears. From the viewpoint of stabilization of the commutation operation and enhancement of the motor efficiency, the optimal range of values of this ratio (θ₂/θ₄) is from 85.7% to 66.7% at which equal motor efficiency is obtained. When this ratio (θ₂/θ₄) is set within such a range of 66.7% to 85.7%, the motor efficient can be enhanced by about 1.5%. An angle corresponding to the lowest value of the ratio (θ₂/θ₄), namely, 66.7% is determined as a value of an angle θ₃ that both outermost-circumferential-side outer end surfaces of the adjacent permanent magnet inserting holes, which are arranged like a letter V, form with the rotor axis.

[0054] Second Embodiment

[0055]FIG. 4 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to a second embodiment of the present invention. As shown in FIG. 2, the difference between the second embodiment shown in FIG. 4 and the first embodiment shown in FIG. 2 resides in that the permanent magnets 10 of the first embodiment are replaced with U-shaped permanent magnets 14 in the second embodiment.

[0056] The second embodiment have effects similar to those of the first embodiment shown in FIG. 1.

[0057] Third Embodiment

[0058]FIG. 5 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to a third embodiment of the present invention. The third embodiment shown in FIG. 5 differs from the first embodiment shown in FIG. 2 in that slits 15 and 16 are formed at points outwardly located from the permanent magnets 10 of each pair, which are arranged like a letter “V”, so that such points are points of intersection of the outer circumference of a section of the rotor and trisectors of the angle θ₄ to be trisected into angles θ₅, θ₆, and θ₇ (that is, θ₄/3=θ₅=θ₆=θ₇).

[0059] In the case of the third embodiment, the armature reaction magnetic flux generated by the armature current is reduced still more, as compared with the first embodiment shaped as illustrated in FIG. 2. Thus, q-axis inductance is reduced still more. Consequently, the armature current commutation is achieved more quickly.

[0060] Fourth Embodiment

[0061]FIG. 6 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to a fourth embodiment of the present invention. The fourth embodiment shown in FIG. 6 differs from the second embodiment shown in FIG. 4 in that slits 15 and 16 are formed at points outwardly located from the permanent magnets 10 of each pair, which are arranged like a letter “V”, so that such points are points of intersection of the outer circumference of a section of the rotor and trisectors of the angle θ₄ to be trisected into angles θ₅, θ₆, and θ₇ (that is, θ₄/3=θ₅=θ₆=θ₇).

[0062] In the case of the fourth embodiment, the armature reaction magnetic flux generated by the armature current is reduced still more, as compared with the second embodiment shaped as illustrated in FIG. 4. Thus, q-axis inductance is reduced still more. Consequently, the armature current commutation is achieved more quickly.

[0063] Fifth Embodiment

[0064]FIG. 7 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to a fifth embodiment of the present invention. The fifth embodiment shown in FIG. 7 differs from the first embodiment shown in FIG. 1 in that a stator slit 17 is formed in a central portion of each of the teeth 3 of the stator 2.

[0065] In the case of the fifth embodiment, each of the stator slits 17 acts in such a way as to reduce the leakage magnetic flux of the permanent magnets 10, as compared with the first embodiment shown in FIG. 1. Thus, torque due to the magnetic flux generated by the magnets is increased. Consequently, the motor efficiency is enhanced.

[0066] Sixth Embodiment

[0067]FIG. 8 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to a sixth embodiment of the present invention. The sixth embodiment shown in FIG. 8 differs from the first embodiment of FIG. 2 in that an angle θ₈ between segments respectively drawn from the rotor axis to both points of intersection of the outer circumferential surface of the rotor 7 and V-shaped recess portions 19 and 20, and an angle θ₂ between segments respectively drawn from the rotor axis to both outermost-circumference-side inner end surfaces of the permanent magnets 10 of each pair, which are arranged like a letter “V”, are set in such a manner as to meet the condition: θ₈<θ₂. Consequently, a convex portion 18 is formed between the permanent magnets 10 of each pair, which are arranged like a letter “V”.

[0068] In the case of the sixth embodiment, both armature reaction magnetic flux generated by an armature current and q-axis inductance are slightly higher than those obtained in the first embodiment shaped as illustrated in FIG. 1. Taking all things into consideration, the q-axis inductance is slightly reduced, as compared with the first embodiment. Thus, the armature current commutation is quickly achieved.

[0069] Seventh Embodiment

[0070]FIG. 9 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to a seventh embodiment of the present invention. The seventh embodiment shown in FIG. 9 differs from the sixth embodiment of FIG. 8 in that slits 15 and 16 are formed at places outwardly located from the permanent magnets 10 of each pair, which are arranged like a letter “V”.

[0071] In the case of the seventh embodiment, armature reaction magnetic flux generated y an armature current is reduced still more, as compared with the case of the sixth embodiment shown in FIG. 8. Thus, the q-axis inductance is reduced still more. Consequently, the armature current commutation is quickly achieved.

[0072] Eighth Embodiment

[0073]FIG. 10 is an enlarged radially sectional view of a rotor 7 of a permanent magnet rotating electric machine according to an eighth embodiment of the present invention. The eighth embodiment shown in FIG. 10 differs from the sixth embodiment of FIG. 8 in that an angle θ₈ between segments respectively drawn from the rotor axis to both points of intersection of the outer circumferential surface of the rotor 7 and V-shaped recess portions 19 and 20 form with a rotor axis, and an angle θ₂ between segments respectively drawn from the rotor axis to both outermost-circumference-side inner end surfaces of the permanent magnets 10 of each pair, which are arranged like a letter “V”, are set in such a manner as to meet the condition: θ₈<θ₂. Moreover, the eighth embodiment differs from the sixth embodiment in that the radial positions of L-shaped recess portions 22 and 23 are shifted from those of the permanent magnet inserting holes 9 of each pair, respectively. Thus, a convex portion 21 is formed between the L-shaped recess portions 22 and 23 of each pair.

[0074] In the case of the eighth embodiment, the armature reaction magnetic flux generated by an armature current and the q-axis inductance are slightly higher that those obtained in the case of the sixth embodiment shown in FIG. 8. Taking all things into consideration, the q-axis inductance is slightly reduced, as compared with the sixth embodiment. Thus, the armature current commutation is quickly achieved.

[0075] In the aforementioned embodiments of the present invention, the adjoining permanent magnets are arranged like a convex “U” or “V” with respect to the rotor axis. Further, nearly V-shaped or L-shaped recess portions are formed between adjacent poles in the outer circumferential portion of the rotor core. Thus, torque due to the magnetic flux generated by the magnets is increased. Moreover, the armature reaction magnetic flux generated by the armature current is reduced. Consequently, the q-axis inductance is reduced. Moreover, the armature current commutation is quickly achieved. Thus, there is provided a permanent magnet rotating electric machine that is stably driven even when a position sensorless inverter in the case of 120 degree energization is used for driving the rotating electric machine.

[0076] Although the preferred embodiments of the present invention have been described above, it should be understood that the present invention is not limited thereto and that other modifications will be apparent to those skilled in the art without departing from the spirit of the invention.

[0077] The scope of the present invention, therefore, should be determined solely by the appended claims. 

What is claimed is:
 1. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, and wherein a nearly V-shaped recess portion is formed between adjacent poles in outer circumferential surface portions of said rotor core.
 2. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a nearly V-shaped recess portion is formed between adjacent poles in outer circumferential surface portions of said rotor core, and wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core.
 3. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein a slit radially extending in said rotor is formed in a central portion of each of said teeth of said stator core, wherein, each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, and wherein a nearly V-shaped recess portion is formed between adjacent poles in outer circumferential surface portions of said rotor core.
 4. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein a slit radially extending in said rotor is formed in a central portion of each of said teeth of said stator core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a nearly V-shaped recess portions is formed between adjacent poles in outer circumferential surface portions of said rotor core, and wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core.
 5. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, and wherein a plurality of nearly V-shaped recess portions, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core.
 6. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a plurality of nearly V-shaped recess portions, each of which is placed between adjacent poles, are formed in outer circumferential surface portions of said rotor core, and wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core.
 7. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, and wherein a plurality of nearly L-shaped recess portions, each of which is placed between adjacent poles, are formed in outer circumferential surface portions of said rotor core.
 8. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, and wherein a plurality of nearly L-shaped recess portions, each of which is placed between adjacent poles, are formed in outer circumferential surface portions of said rotor core, and wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core.
 9. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein a slit radially extending in said rotor is formed in a central portion of each of said teeth of said stator core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, and wherein a plurality of nearly V-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core.
 10. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein a slit radially extending in said rotor is formed in a central portion of each of said teeth of said stator core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a plurality of nearly V-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, and wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core.
 11. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein a slit radially extending in said rotor is formed in a central portion of each of said teeth of said stator core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, and wherein a plurality of nearly L-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core.
 12. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein a slit radially extending in said rotor is formed in a central portion of each of said teeth of said stator core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a plurality of nearly L-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, and wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core.
 13. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a plurality of nearly V-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, wherein a convex portion core is placed between said plurality of nearly V-shaped recess portions formed in outer circumferential surface portions of said rotor core, and wherein width of an innermost-circumference-side part of said convex portion core is larger than an outermost-circumference-side circumferential distance between said permanent magnet inserting holes.
 14. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a plurality of nearly V-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core, wherein a convex portion core is placed between said plurality of nearly V-shaped recess portions formed in outer circumferential surface portions of said rotor core, and wherein width of an innermost-circumference-side part of said convex portion core is larger than an outermost-circumference-side circumferential distance between said permanent magnet inserting holes.
 15. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a plurality of nearly L-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, wherein a convex portion core is placed between said plurality of nearly L-shaped recess portions formed in outer circumferential surface portions of said rotor core, and wherein width of an innermost-circumference-side part of said convex portion core is larger than an outermost-circumference-side circumferential distance between said permanent magnet inserting holes.
 16. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a plurality of nearly L-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core, wherein a convex portion core is placed between said plurality of nearly L-shaped recess portions formed in outer circumferential surface portions of said rotor core, and wherein width of an innermost-circumference-side part of said convex portion core is larger than an outermost-circumference-side circumferential distance between said permanent magnet inserting holes.
 17. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein a slit radially extending in said rotor is formed in a central portion of each of said teeth of said stator core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a plurality of nearly V-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, wherein a convex portion core is placed between said plurality of nearly V-shaped recess portions formed in outer circumferential surface portions of said rotor core, and wherein width of an innermost-circumference-side part of said convex portion core is larger than an outermost-circumference-side circumferential distance between said permanent magnet inserting holes.
 18. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein a slit radially extending in said rotor is formed in a central portion of each of said teeth of said stator core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a plurality of nearly V-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core, wherein a convex portion core is placed between said plurality of nearly V-shaped recess portions formed in outer circumferential surface portions of said rotor core, and wherein width of an innermost-circumference-side part of said convex portion core is larger than an outermost-circumference-side circumferential distance between said permanent magnet inserting holes.
 19. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein a slit radially extending in said rotor is formed in a central portion of each of said teeth of said stator core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a plurality of nearly L-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, wherein a convex portion core is placed between said plurality of nearly L-shaped recess portions formed in outer circumferential surface portions of said rotor core, and wherein width of an innermost-circumference-side part of said convex portion core is larger than an outermost-circumference-side circumferential distance between said permanent magnet inserting holes.
 20. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein a slit radially extending in said rotor is formed in a central portion of each of said teeth of said stator core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a plurality of nearly L-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core, wherein a convex portion core is placed between said plurality of nearly L-shaped recess portions formed in outer circumferential surface portions of said rotor core, and wherein width of an innermost-circumference-side part of said convex portion core is larger than an outermost-circumference-side circumferential distance between said permanent magnet inserting holes.
 21. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a nearly V-shaped recess portion is formed between adjacent poles in outer circumferential surface portions of said rotor core, and wherein a ratio (θ₂/θ₄) of an angle θ₂ between segments respectively drawn from said rotor axis to both points of intersection of said outer circumferential surface of said rotor core and said V-shaped recess portion, to a value θ₄ obtained by dividing 360 (deg.) by the number of poles is set so that 66.7%≦(θ₂/θ₄)≦85.7%.
 22. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a nearly V-shaped recess portion is formed between adjacent poles in outer circumferential surface portions of said rotor core, wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core, and wherein a ratio (θ₂/θ₄) of an angle θ₂ between segments respectively drawn from said rotor axis to both points of intersection of said outer circumferential surface of said rotor core and said V-shaped recess portion, to a value θ₄ obtained by dividing 360 (deg.) by the number of poles is set so that 66.7%≦(θ₂/θ₄)≦85.7%.
 23. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein a slit radially extending in said rotor is formed in a central portion of each of said teeth of said stator core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a nearly V-shaped recess portion is formed between adjacent poles in outer circumferential surface portions of said rotor core, and wherein a ratio (θ₂/θ₄) of an angle θ₂ between segments respectively drawn from said rotor axis to both points of intersection of said outer circumferential surface of said rotor core and said V-shaped recess portion, to a value θ₄ obtained by dividing 360 (deg.) by the number of poles is set so that 66.7%≦(θ₂/θ₄)≦85.7%.
 24. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein a slit radially extending in said rotor is formed in a central portion of each of said teeth of said stator core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a nearly V-shaped recess portion is formed between adjacent poles in outer circumferential surface portions of said rotor core, wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core, and wherein a ratio (θ₂/θ₄) of an angle θ₂ between segments respectively drawn from said rotor axis to both points of intersection of said outer circumferential surface of said rotor core and said V-shaped recess portion, to a value θ₄ obtained by dividing 360 (deg.) by the number of poles is set so that 66.7%≦(θ₂/θ₄)≦85.7%.
 25. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, and wherein a plurality of nearly V-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, and wherein a ratio (θ₂/θ₄) of an angle θ₂ between segments respectively drawn from said rotor axis to both points of intersection of said outer circumferential surface of said rotor core and said V-shaped recess portion, to a value θ₄ obtained by dividing 360 (deg.) by the number of poles is set so that 66.7%≦(θ₂/θ₄)≦85.7%.
 26. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, and wherein a plurality of nearly V-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core, and wherein a ratio (θ₂/θ₄) of an angle θ₂ between segments respectively drawn from said rotor axis to both points of intersection of said outer circumferential surface of said rotor core and said V-shaped recess portion, to a value θ₄ obtained by dividing 360 (deg.) by the number of poles is set so that 66.7%≦(θ₂/θ₄)≦85.7%.
 27. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, and wherein a plurality of nearly L-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, and wherein a ratio (θ₂/θ₄) of an angle θ₂ between segments respectively drawn from said rotor axis to both points of intersection of said outer circumferential surface of said rotor core and said L-shaped recess portion, to a value θ₄ obtained by dividing 360 (deg.) by the number of poles is set so that 66.7%≦(θ₂/θ₄)≦85.7%.
 28. A permanent magnet rotating electric machine comprising a stator, into which concentratively wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets accommodated into a plurality of permanent magnet inserting holes formed in a rotor core, wherein each pair of adjacent ones of said permanent magnets is arranged like a convex V or said permanent magnets are convex and U-shaped with respect to a rotor axis, wherein a plurality of nearly L-shaped recess portion s, each of which is placed between adjacent poles of each pair, are formed in outer circumferential surface portions of said rotor core, and wherein a plurality of slits radially extending in said rotor are formed in an outer circumferential portion, which is located outwardly from said permanent magnets, of said rotor core, and wherein a ratio (θ₂/θ₄) of an angle θ₂ between segments respectively drawn from said rotor axis to both points of intersection of said outer circumferential surface of said rotor core and said L-shaped recess portion, to a value θ₄ obtained by dividing 360 (deg.) by the number of poles is set so that 66.7%≦(θ₂/θ₄)≦85.7%. 